With the widespread of information communication services, the introduction of various multimedia services and high-quality services, the demand of communication services is rapidly increasing. In order to actively cope with the above-mentioned situation, capacity of a communication system must be greatly increased.
The above-mentioned requirements are more significant in a wireless communication technical field than in a wired communication technical field, because the available frequency resources of the wireless communication field are limited and must be shared with each other to effectively employ the limited frequency resources. In addition, the demands of the wireless communication technology are rapidly increasing due to the advantages of the wireless communication technology.
In recent times, Space Time Coding (STC) techniques have been proposed to improve the efficiency of radio resources. The STC technique mounts a plurality of antennas to a transceiver (i.e., a transmission/reception unit) to acquire an additional spatial area for employing resources, increases communication-link reliability based on a diversity gain without increasing a bandwidth, or increases transmission (Tx) capacity via parallel transmission based on spatial multiplexing.
A basic system capable of increasing the transmission capacity or acquiring the diversity gain will hereinafter be described in detail.
FIG. 1 is a block diagram illustrating an orthogonal frequency division multiplexing system including a single transmission/reception antenna.
FIG. 2 is a block diagram illustrating the OFDM system including a multiple Tx/Rx (i.e., transmission/reception) antennas.
Referring to FIG. 1, a transmission end of the OFDM system including a single Tx/Rx antenna includes a channel encoder 101, a mapper 102, and a serial-to-parallel (S/P) converter 103. Referring to FIG. 2, a transmission end of the OFDM system including multiple Tx/Rx antennas includes a channel encoder 101′, a mapper 102′, and a serial-to-parallel (S/P) converter 103′.
Referring to FIG. 1, a reception end of the OFDM system includes a parallel-to-serial (P/S) converter 106, a demapper 107, a channel decoder 108, and a data estimator 109. Referring to FIG. 2, a reception end of the OFDM system includes a parallel-to-serial (P/S) converter 106′, a demapper 107′, a channel decoder 108′, and a data estimator 109′.
If the system is a multi-antenna system, the above-mentioned transmission end further includes a multi-antenna encoder 104′, and the above-mentioned reception end further includes a multi-antenna decoder 105′.
The channel encoder 101 or 101′ attaches a redundant bit to a data bit to reduce the channel effect or the noise effect. The mapper 102 or 102′ converts data bit information into data symbol information. The S/P converter 103 or 103′ converts serial data into parallel data.
In the meantime, the multi-antenna encoder 104′ converts a data symbol into a space-time signal. In the case of a multi-antenna, a transmission (Tx) antenna transmits the space-time signal over a channel.
In this case, the multi-antenna decoder 104′ transmits the same signal over the multi-antenna to acquire a diversity gain. In order to increase a transfer rate, the multi-antenna encoder 104′ transmits different signals over individual multiple antennas.
In the meantime, the reception (Rx) antenna receives a signal over a channel. Also, the multi-antenna decoder 105′ converts the received space-time signal into each data symbol. The demapper 107 or 107′ converts the data symbol into bit information. The P/S converter 106 or 106′ converts the parallel signal into the serial signal. Finally, the channel decoder 108 or 108′ decodes the channel code, and performs channel estimation.
The OFDM system including the above-mentioned transmission/reception unit employs the STC technique for use in a multi-antenna system to acquire the diversity gain. In more detail, the STC technique is a technique for acquiring the spatial diversity gain by re-transmitting the same signal over other antennas, when continuously transmitting the same signal under the multi-antenna environment. The following equation 1 indicating the most principal space-time code (STC) is applied to the system including two Tx antennas.
                              1                      2                          ⁡                  [                                                                      S                  1                                                                              -                                      S                    2                    *                                                                                                                        S                  2                                                                              S                  1                  *                                                              ]                                    [                  Equation          ⁢                                          ⁢          1                ]            
In Equation 1, two rows indicate data transmitted over two antennas, respectively, and two columns indicate data transmitted over individual antennas during each time slot. In the case of using the above-mentioned STC technique, the OFDM system can acquire a high space-time diversity gain. However, as shown in Equation 1, the receiver for receiving data requires a data combiner for combining first data received from a first antenna with second data received from a second antenna, and a data detector for detecting original data via the data combiner, such that the receiver may be unavoidably complicated.
In the meantime, a Cyclic Delay Diversity (CDD) technique has been proposed to solve the problems of the above-mentioned STC technique. However, the CDD technique can acquire only the diversity based on channel characteristics of a frequency axis.
Therefore, there is needed an improved data communication technique for transmitting/receiving data with time-diversity or data with time-frequency diversity using a simple receiver.